Method for nondestructive testing by using a defocussed electron beam



2 Sheets-Sheet 1 R. A. DI CURCIO ETA METHOD FOR NONDESTRUCTIVE TESTIN E BY USING A DEFOCUSSED ELECTRON BEAM MTRDQ- XR 381628767 Dec. 22,1964

Filed Sept. 4, 1962 Z- I lien-I522...

W/LLAED FT JT/ -2 1964 R. A. D! CURCIO ETAL 3,162,767

us'moo FOR uouoss'raucnva TESTING BY usmc A DEFOCUSSEID ELECTRON BEAM Filed Sept. 4, 1962 2 Sheets-Sheet 2 MaUh United States Patent 3,162,767 METHOD FOR NONDESTRUCTIVE TESTING BY USING A DEFOCUSSED ELECTRON BEAM Robert A. Di Curcio, Windsor, and Willard F. Stillwell, Jr., Thompsonville, Conn.. assignors to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Sept. 4, 1962, Ser. No. 220,987 2 Claims. (Cl. 250-495) Our invention relates to the manufacture and testing of thin film microelectronic components. More particularly, our invention relates to scribing thin film electronic components with a beam of charged particles and thereafter utilizing the same beam for non-destructive testing of the scribed components.

The method of our invention is particularly applicable for use with an electron beam machine. Electron beam machines, as they are generally known, are devices which use the kinetic energy of an electron beam to work a material. U.S. Patent No. 2,944,172, issued July 5, 1960, to W. Optiz et al., discloses such a machine. These machines operate by generating a highly focused beam of electrons in a vacuum chamber. The electron beam is a welding, cutting and machining tool which has practically no mass but has high kinetic energy because of the extremely high velocity imparted to the electrons. Transfer of this kinetic energy to the lattice electrons of the workpiece, which is usually but not necessarily also located in the vacuum chamber, generates higher lattice vibrations which cause an increase in the temperature within the impingement area sutficient to accomplish work.

Electron beam machines are particularly advantageous tools for use in the production of microelectronic components. A number of characteristics of these machines are quite unique and thus add significantaly to their utility. For example, with an electron beam it is possible to achieve extremely high power density, up to ten billion watts per square inch. As is well known in the art, beam power density is a function of beam current. electron accelerating voltage and beam focus or spot size. With such power density the beam can locally heat, fuse, or vaporize materials as desired. These processes can be easily and precisely controlled since the cross-sectional diameter of the beam can be varied from tenths of a thousandth of an inch up to many thousandths. Also, the power input of the beam can be varied from less than a watt up to many kilowatts, and since the beam can be focused and deflected by electrical means, the position or point of impingement of the beam upon the workpiece can be controlled with extreme accuracy. Further, electron beam processes are extremely pure in a chemical sense. Electrons do not have chemical or material properties and since these processes are normally carried out in a high vacuum the concentration of foreign atoms is extremely low.

In the prior art, the manufacture of thin film electronic components was a three step process. The first step comprised the vapor deposition of the thin film on a substrate. U.S. Patent No. 2,746,420, issued May 22, 1956, to K. H. Steigcrwald. discloses an apparatus utilizing an electron beam as the heat source for evaporating the material to be deposited as a thin film.- The vapor deposition process was followed by the step of scribing the dcsircd components in the film. This step usually entailed removing the coated substrate from the vacuum chamber of the vapor deposition apparatus, masking the film and utilizing a chemical etching process to locally remove portions of the film. The third step consisted of nondestructive testing of the components formed in the etching step. Prior to our invention, this testing step consisted merely of an electrical continuity test or resistance 3,162,767. Patented Dec. 22, 1964 ice measurement which often failed to reveal tiny cracks or flaws in the film which would cause failure of the component during use in its intended environment. There is no technique available in the prior art. not even tedious examination under a microscope. which will permit detection of microscopic discontinuities, faults, cracks and flaws that can cause failure of thin film devices. In fact, quality control of a thin film component manufacturing process is virtually impossible since even when an electrical test indicates a defective component the cause of the defect can usually not be determined.

Our invention overcomes the above-mentioned disadvantages of the prior art by providing a continuous process for the fabrication and testing of thin film electronic components which allows faster and more accurate fabrication of these components and which permits testing the thus formed components for microscopic flaws.

it is therefore an object of our invention to manufacture and test thin film electronic components.

It is another object of our invention to utilize a beam of charged particles for both the fabricating and testing of thin film electronic components.

It is yet another object of our invention to test thin film electronic components for microscopic flaws.

It is also an object of our invention to provide a continuous process for the manufacture and nondestructive testing of thin film electron components.

These and other objects of our invention are preferably accomplished in a continuous process performed in an evacuated work chamber. The process comprises directing a beam of charged particles against an evaporant causing it to be heated and thus vaporized. The vapor thus formed will condense on a plurality of substrates which have been properly positioned in the chamber above the evaporant. The coated substrates are then repositioned in the chamber so as to be in the line of the beam of charged particles and the focus and intensity of the beam are readjusted. The beam is then directed across the surface of the substrate in a prescribed manner so as to trace the desired thin film component. The small diameter, high intensity moving beam causes local evaporation of discrete lines of the film and thus etches the component. Next. the beam is defocused or its power density otherwise reduced by decreasing the beam intensity by downwardly adjusting beam current and/or acceleration voltage, and the defocused beam played across the surface of the film. An essential feature of this invention lies in our discovery that a low power density electron beam will cause the substrate, which is usually a ceramic such as alumina, to fiouresce brightly. By using a microscope associated with the charged particle generator, the fluorescent substrate can be observed and fiaws or discontinuities in the film will be readily apparent to the operator.

Our invention may be better understood and its numerous advantages will become apparent to those skilled in the art by reference to the accompanying drawing in which:

FIGURE 1 discloses an electron beam generator adapted to be used in the performance of our invention.

FIGURE 2 is a view of the evacuated work chamber of the device of FlGURl-I l.

FIGURE 3 is an end view of the charge carrier shown in FIGURES 1 and 2.

FIGURE 4 is an enlarged view of a thin film resistor fabricated and tested in accordance with our invention.

Referring now to FlGURE 1, an electron beam machine is shown having an electron gun chamber 10, a beam focusing column 12 and an evacuated work chamber 14. inside electron gun chamber 10 there is a directly heated cathode 16 for emitting electrons which are accelerated down column 12 by a difference in potential between cathode 16 and anode 18. Surrounding cathode 16 is a grid cup 20 which is biased at a voltage which is more negative than the voltage applied to cathode 16. The magnitude of this bias controls the beam current while, due to the shape of the grid. lllsr) aiding in the focusing of the beam. The electrons which are accelerated down column 12 are focused into a narrow beam, indicated by reference numeral 22, by upper adjusting coil 24, lower adjusting coil 26, magnetic lens assembly 29 and upper and lower diaphragms 28 and 30. The beam 22 passes down a tube 32, which is suspended in column 12, into work chamber 14 where it impinges upon the work and consequently, gives up its kinetic energy in the form of heat. The material to be worked may be moved beneath the beam and the beam may be deflected over limited areas of the material by means of deflection coils 34. The material being worked is observed visually through an optical viewing system, part of which is not shown, comprising a viewing light 38 which is focused on the material by mirrors 40 and 42. The light path is shown as a dashed line 46. The image of the work is transmitted back up the light path, reflected by mirrors 40 and 42, and transmitted via optical column 48 which includes lens 50 to a system including a microscope, not shown, wherein it is enlarged and viewed by an operator. Positioned between beam column 12 and optical column 48 is a piece of leaded glass 52 which protects the operator from X-rays gen-- erated during the electron beam operation.

Located in work chamber 14 is an apparatus for supporting and positioning the substrates which are to be coatedand scribed. This apparatus consists of a device 60 preferably having the shape of a portion of a cylinder. Afiixed to one end of device 60 is a circular gear 62 which is engaged by gear 63 which is in turn driven by a motor, not shown. The device 60 and gear 62 are supported in the work chamber by and are rotatable about member 64 and shaft 66. Attached to the inner surface of device 60 are a pair of supports 68 and 70 on which are afiixed by suitable means the substrates to be coated and then scribed. Also located in chamber 14 is a movable table 72 which rides on a track 74. Table 72 is adapted to carry a crucible 76 which, as can be clearly seen from FIGURE 3, extends from one side of the table. Crucible 76 is counterbalanced by a weight 78.

The performance of our novel process is accomplished in the following manner. The substrates to be coated are positioned on supports 68 and 70 and device 60 is rotated so that a hole 61 in the top thereof is aligned with the axis of the beam 22. The crucible 76 is loaded with the evaporant and is then positioned by table 72 so as to also be in line with beam 22 which will pass through hole 61. Work chamber 14 is then evacuated by means not shown and the beam intensity and focus controls on the electron beam generator are adjusted to the values necessary to cause evaporation of the material in crucible 76. The beam generator is then activated and the beam impinges upon the evaporant causing it to vaporize. The vapors rising from crucible 76 will condense upon the substrates carried by supports 68 and 70. This step is depicted by FIGURES 2 and 3. By proper selection of the angles and spacial relation between the supports and the crucible, an even film will be deposited on the substrates. It is, of course, understood that the substrate may be masked to prevent vapor from being deposited in certain regions such as a margin around the edges. As taught by the above-mentioned patent to Steigerwald, in order to control the thickness of the deposited layer and to finish the evaporation when a predetermined thickness or shape of the layer has been reached, the thickness of the film on the substrate can be monitored by means of photoelectric devices which sense the brightness and color of a light source as it appears through a transparent surface which is also exposed to the vapor emanating from the crucible. The

photoelectric devices may be used to gate a control circuit for automatically causing the beam 22 to be biased oil when the film has achieved the desired thickness.

When the desired thickness film has been deposited on the substrate, the beam generator is deactivated and table 72 is moved back out of the way. As can be seen from FIGURE 1. device 60 is then rotated until a first one of the supports 68 is aligned with the beam axis. The controls of the beam generator are then reset so that a highly focused, intense beam will be produced. The beam generator is reactivated and the beam deflected across the surface of the substrate by means of varying the current supplied to deflection coils 34. This step may be carried on manually by an operator viewing the work through the optical system or the beam deflection maybe programmed by computer means known in the art. The intense moving beam will scribe, by local evaporation, discrete lines or patterns on the previously deposited film. Line widths of approximately 0.0007 inch located on three mil centers can be produced. FIG- URE 4 shows a typical thin film indicator which has been electron beam scribed to a precisely predetermined resistance value. The actual size of the resistor shown in FIGURE 4 is .35 inch square and .01 inch thick. Of course, thin film inductors and capacitors may also be produced by this method. In the device of FIGURE 4, leads would be attached to the contact pads indicated by reference numerals 80 and 82. At this point in the process, if desired, the leads which may have previously been positioned against the contact pads can be welded to the thin film device with the electron beam.

After the scribing step has been completed, the electron beam is either defocused or its intensity reduced. A particularly novel feature of this invention is permitted by our discovery that a low power density beam of high energy electrons such as that available from an electron beam cutting or welding machine will cause a substrate upon which the beam impinges to fluoresee brilliantly, thereby revealing flaws of discontinuities that would be completely invisible even under high magnification and otherwise undectatable. In a typical example wherein thin film resistors comprised of a chromium film deposited on an alumina (A1 0 substrate were scribed in an electron beam welder manufactured by the Carl Zeiss Foundation of West Germany, the machine parameters were set so as to provide an electron beam having between 40 and 60 microamperes of beam current with an acceleration voltage kv. Thereafter, the testing pro cedure was accomplished, while maintaining the aforementioned beam current and acceleration voltage, by changing the spot size from a one and one-half mil diameter beam utilized for scribing to a 30 mil diameter beam for testing by reducing the current to the magnetic lens assembly from 90 milliamperes to between 5 and 10 milliamperes. The defocused beam is played back and forth across the surface of the thin film component by varying the current to deflection coils 34 while the component is viewed by the operator through the optical system. Flaws and discontinuities are made readily visible during this step even when the thin film component is covered by protective SiO. The film will mask the fluorescence and thus light will appear only in areas where the beam has scribed a line or where there is a defect in the film. For example, the hair-line cracks in the film indicated at 84, which cracks have been greatly exaggerated in size, will pass light from the fluorescent substrate and will thus. due in part to the contrast with the uncracked film, be readily apparent to the operator. The cracks indicated at 84 would not be revealed by resistance measurements or examination with a microscope and would, in the case of vibration, spread thereby causing failure of the component. Not only does the fluorescence produced by the defocused beam reveal inherent tlaws in metallic coatings, but it also serves as a valuable method of visually observing the thin film component in order to determine whether the metal film is completely removed from the scribed areas, whether the appropriate pads are completely isolated, and whether the scribing has initiated incipient discontinuities in the resistant film. This step will also yield information as to the surface condition of the substrate. For example, virgin alumina fluoresccs light red, but fiuoresces green after being lightly fused with an electron beam bombardment, and this green will change to blue with violet bombardment which produces more pronounced fusion of the surface.

From the above description, it should be apparent to those skilled in the art that our invention provides a valuable tool for use in the manufacture and testing of microelectronic devices. In regards to the testing aspects, our invention has proved to be exceptionally valuable in testing both devices made in the manner described above and also devices made by other processes and then placed in the electron beam machine for examination. That is, our invention has utility in connection with investigations concerning the properties of all thin metallic films vapor deposited or otherwise deposited on substrates such as alumina, various metalized layers such as moly-manganese fired on substrates, and electron beam or otherwise scribed thin film components. Thus, while a preferred embodiment has been shown and described, various modifications and substitutions may be made without deviating from the scope and spirit of our invention. Therefore, our invention is described by way of illustration rather than limitation and accordingly it is understood that our invention is to be limited only by the appended claims taken in view of the prior art.

We claim:

1. A method for the nondestructive testing of electronic circuit components which have been fabricated by the deposition of at least one film of conductive or semiconductive material on the surface or surfaces of a nonconductive substrate comprising:

generating a beam of electrons,

placing the component to be tested generally in the path of the beam,

adjusting the power density of the beam to a value which will cause the substrate material to fluoresce. deflecting the beam across the surface of the component, and

observing the fluorescence emanating from the component during the deflection whereby defects in the film will be readily apparent.

2. The method of claim 1 wherein the step of placing the component generally in the path of the beam of electrons comprises:

placing the component to be tested in the vacuum chamber of an electron beam machine,

positioning the component in the vacuum chamber so as to be in line with the electron beam generated by the machine.

References Cited by the Examiner UNlTED STATES PATENTS 1,640,567 8/27 Firestone 73 104 2,259,400 10/41 Switzer 250-41 2,746,420 5/56 Steigerwald 11849.l

3,049,618 8/62 Thome 250-495 FOREIGN PATENTS 125,392 5/59 Russia.

OTHER REFERENCES Electronic Engineering, December 1946, pp. 361-7, p. 362 relied on.

Mollenstedt: Proc. of Third Symposium on Electron Beam Processes Alloyd Electronics Corp., March 23 and 24, 1961, Boston, pp. 340-357.

RICHARD D. NEVIUS, Primary Examiner. 

1. A METHOD FOR THE NONDESTRUCTIVE TESTING OF ELECTRONIC CIRCUIT COMPONENTS WHICH HAVE BEEN FABRICATED BY THE DEPOSITION OF AT LEAST ONE FILM OF CONDUCTIVE OR SEMICONDUCTIVE MATERIAL ON THE SURFACE OR SURFACES OF A NONCONDUCTIVE SUBSTRATE COMPRISING: GENERATING A BEAM OF ELECTRONS, PLACING THE COMPONENT TO BE TESTED GENERALLY IN THE PATH OF THE BEAM, ADJUSTING THE POWER DENSITY OF THE BEAM TO A VALUE WHICH WILL CAUSE THE SUBSTRATE MATERIAL TO FLUORESCE, DEFLECTING THE BEAM ACROSS THE SURFACE OF THE COMPONENT, AND OBSERVING THE FLUORESCENCE EMANATING FROM THE COMPONENT DURING THE DEFLECTION WHEREBY DEFECTS IN THE FILM WILL BE READILY APPARENT. 